AE3D Export - Maya, Max, and Lightwave

Simply select the layers you want to export and the plug in with spit out a text file that can be read by Maya, 3ds Max, or Lightwave. It will export any camera, and turn any other AE layer into a null/dummy/locator object in the 3D packages. This should work on almost all AE animations, including ones that have parenting, auto-orientation, and even non-uniform scaling. There are a few rare cases where it won't work, like with negative scale values, or when layers get "sheared" (this happens with a combination of non-uniform scaling, parenting, and rotation, causing rectangles to "lean"...it's best avoided anyway!).

Difference Matte Effect Tutorial

The Difference Matte effect creates a transparency a mask or a matte by comparing the pixels in a source layer with the pixel in a defined difference layer, and then keying out (eliminating) pixels in the source layer that match both the position and color in the difference layer.